Myeloid differentiation will be investigated using regulated complementary DNA (cDNA) clones of the HL-60 myeloid cell line; that is, clones that represent mRNA that change in abundance as HL-60 differentiates. The common and divergent pathways of gene expression will be examined as HL-60 differentiates from promyelocytes to granulocytes and from promyelocytes to macrophage-like cells. Of special interest will be the study of the molecular modulation of lysozyme and myeloperoxidase (MPO) expression. The human MPO and lysozyme cDNA clones will be isolated, a restriction endonuclease map of the genomic genes determined, and the genes assigned to precise chromosomal locations. The role of DNA methylation and chromatin structure in myeloid differentiation will be examined. The molecular defect(s) of hereditary and secondary MPO deficiency in man will be studied. Myeloid differentiation will also be examined by studying the interaction of differentiating inducing factor (DIF) with myeloid cells. We shall identify a rich source of DIF and develop a rapid assay for DIF. The DIF will be purified and partially characterized. The principal questions will be: Can DIF induce differentiation of different classes of myeloid leukemic cells in vitro and/or in vivo; and what is the mechanism by which DIF induces myeloid cells to differentiate? The study will be facilitated by using human myeloid leukemic cell lines that have different abilities to differentiate in the presence of DIF. The planned studies should provide a better understanding of the control of proliferation and differentiation in acute myelogenous leukemia and, in a broader perspective, the control of normal cellular growth and differentiation.